It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the inci...It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller （≥ 20°）. Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method （TSM） and the method of moment （MOM） are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.展开更多
利用全球导航卫星反射信号(Global Navigation Satellite System Reflectometry,GNSS-R)进行海洋环境要素探测已成为国内外遥感领域一大热点。镜面反射点作为GNSS-R遥感探测的坐标基准,其预测的精度与速度对后续环境要素的反演有着显著...利用全球导航卫星反射信号(Global Navigation Satellite System Reflectometry,GNSS-R)进行海洋环境要素探测已成为国内外遥感领域一大热点。镜面反射点作为GNSS-R遥感探测的坐标基准,其预测的精度与速度对后续环境要素的反演有着显著影响。针对星载GNSS-R实时预测高精度镜面反射点的需求,提出了一种基于AdaGrad优化的GNSS-R镜面反射点自适应预测算法。利用空间几何关系对镜面反射点进行粗略估计,通过预处理后利用AdaGrad优化寻找镜面反射点的最优解,仿真实验证明算法的精确性、高效性。展开更多
从全球导航卫星系统反射信号(Global Navigation Satellite System Reflectometry,GNSS-R)测高应用中对镜面反射点的高精度需求出发,利用GNSS-R空间几何位置关系和机器学习中的RMSprop(Root Mean Square Prop)算法对镜面反射点问题进行...从全球导航卫星系统反射信号(Global Navigation Satellite System Reflectometry,GNSS-R)测高应用中对镜面反射点的高精度需求出发,利用GNSS-R空间几何位置关系和机器学习中的RMSprop(Root Mean Square Prop)算法对镜面反射点问题进行研究,提出了一种基于RMSprop的高精度镜面反射点预测算法,该算法能够实现对学习率的自适应调整,加速梯度下降,提高算法的收敛性能。仿真结果表明,该算法收敛快,精度高。展开更多
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.40906088)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.200804231021)
文摘It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller （≥ 20°）. Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method （TSM） and the method of moment （MOM） are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.
文摘利用全球导航卫星反射信号(Global Navigation Satellite System Reflectometry,GNSS-R)进行海洋环境要素探测已成为国内外遥感领域一大热点。镜面反射点作为GNSS-R遥感探测的坐标基准,其预测的精度与速度对后续环境要素的反演有着显著影响。针对星载GNSS-R实时预测高精度镜面反射点的需求,提出了一种基于AdaGrad优化的GNSS-R镜面反射点自适应预测算法。利用空间几何关系对镜面反射点进行粗略估计,通过预处理后利用AdaGrad优化寻找镜面反射点的最优解,仿真实验证明算法的精确性、高效性。
文摘从全球导航卫星系统反射信号(Global Navigation Satellite System Reflectometry,GNSS-R)测高应用中对镜面反射点的高精度需求出发,利用GNSS-R空间几何位置关系和机器学习中的RMSprop(Root Mean Square Prop)算法对镜面反射点问题进行研究,提出了一种基于RMSprop的高精度镜面反射点预测算法,该算法能够实现对学习率的自适应调整,加速梯度下降,提高算法的收敛性能。仿真结果表明,该算法收敛快,精度高。
